The ability to produce complex patterns of molecules on surfaces is important for understanding a number of different phenomena including dewetting, adhesion, cell-surface interactions, and cell-cell interactions; it is also significant for developing applications in biology and biochemistry, such as assays, microarrays, and devices for high-throughput screening.
Several techniques allow the alignment of molecules, and in particular, the alignment of SAMs, on surfaces. Microcontact printing (μCP) of alkanethiols on a gold or silver surface using a poly(dimethylsiloxane) (PDMS) stamp allows one type of alkanethiol SAM to be patterned in the background of a second type of alkanethiol. Multiple printing steps can produce multiple patterns of molecules on a surface, but most patterns require the alignment of a stamp. Micromolding in capillaries (MIMIC) is a general method for depositing polymers, SAMs, and proteins in continuous patterns on a substrate, but MIMIC is unable to align multiple, discontinuous patterns. Three-dimensional networks of channels in PDMS can generate multiple, discontinuous patterns of proteins and cells, but the microfluidic networks require alignment in fabrication. Chen et al. have demonstrated an elegant technique using a multilevel PDMS stamp to print multiple, aligned regions of proteins. This technique involves several complicated steps (in fabrication of the stamp, in inking, and in printing or patterning).
A number of procedures for multicolor patterning have used photolithography. In one report, different fluorescent dyes were coupled in solution to a surface coated with bovine serum albumin (BSA) using irradiation with UV light through a photomask. Where light passed through the photomask, the fluorescent dye molecules were excited and produced radicals; fluorescent dye radical molecules coupled to BSA in regions defined mostly by the pattern of illumination. Although this method permitted multiple molecules to be patterned by using different wavelengths to excite different fluorescent dyes, alignment of individual patterns was not demonstrated, and the resolution of the features was limited by the diffusion of the fluorescent dyes. Another report described the use of diarylethene derivatives that undergo photoinduced structural rearrangements depending on the wavelength of light used. Two diarylethene derivatives were cast as a film and exposed sequentially through individual masks to UV or visible light.
The examples above show that many existing techniques require alignment of two (or more) features when fabricating either a photomask or a microfluidic device (e.g., photolithography, MIMIC) or alignment of a stamp when printing patterns of molecules (e.g., μCP, microcontact printing), in order to fabricate multiple patterns of molecules on a surface. There remains a general need in the art for improved methods of fabricating multiple patterns on a surface, without multiple steps of alignment.